1. Field of the Invention
This invention relates to a propulsion unit that comprises systems for tapping hot air whose purpose is to reduce the sound emission of said power plant.
2. Description of the Related Art
FIGS. 1 and 2 show a propulsion unit of an aircraft that comprises a nacelle 10 in which a power plant 12, connected by means of a mast to the rest of the aircraft, is arranged essentially concentrically.
The nacelle 10 comprises an inside wall that delimits a pipe 14 with an air intake 16 at the front, whereby a first portion of the incoming air stream, called a primary stream, passes through the power plant 12 to assist the combustion, and whereby the second portion of the air stream, called the secondary stream, is entrained by a fan 18 and flows into an annular pipe 20 that is delimited by the inside wall of the nacelle and the outside wall of the power plant.
The power plant 12 comprises an exhaust system, for example for preventing “pumping” phenomena of the power plant at takeoff, whereby said system makes it possible to tap air at a first tapping point 22 in the combustion chamber and to eject it outside of the power plant 12. For this purpose, the power plant comprises a pipe 24 that is equipped with a valve 26 for directing the air under certain conditions from the first tapping point 22 to the delivery zone, outside of the power plant via an orifice 28 that empties into the annular pipe 20, in particular via a large number of orifices that are made in the nozzle. This system is called a “pepper pot.”
This ejection into the annular pipe 20 has the major drawback of emitting noise.
In parallel, the propulsion unit can comprise a pneumatic-type frost treatment system whose purpose is to tap hot air at the power plant and to deliver it to the air intake 16. Such a system is described in particular in the document EP-1,232,944.
This frost treatment system comprises at least one pipe 30 that is optionally equipped with means for adjusting the flow rate 32 to direct the hot air from a second tapping point 34 into the power plant toward the air intake. After having circulated at the air intake to achieve defrosting, the hot air is discharged into the air passage that enters into the pipe 14 of the nacelle. The delivery of the hot air that is used for defrosting the air intake does not generate noise pollution.